This invention relates to digital computers, and more particularly relates to computers having internal hard disk drive units.
Computers of the desktop size for personal or business usage being designed today often include an internal hard disk drive unit providing relatively fast access bulk memory storage for the computer system. Currently, the microprocessors commonly used in computers of this type are 32-bit devices; that is, memory addresses and data take the form of 32-bit binary numbers which can be transferred along correspondingly sized address and data busses in the computer. For this reason, the maximum size of (byte addressable) main memory in these machines is 2.sup.32 =4-Gigabytes.
Even though an address range of 4-Gbyte is available, 32-bit computers are not provided with a fully-populated main memory; this much memory is of prohibitive size and cost, and is not needed for typical business applications. Instead, 32-bit machines may include only 1- of 2-Mbyte or so of DRAM storage, and may employ techniques of virtual memory management, such as "demand paging" to increase the effective size of the DRAM. In one typical way of using virtual memory techniques, the storage facilities provided by I/O modules such as disk drives are merged with the main memory address space to form a larger "virtual memory space". The virtual memory space is subdivided into numerous "pages" or "segments" of either fixed or variable size. At any one time, only a limited sub-set (one or more) pages or segments can be stored in the main memory DRAM of the computer, while the remaining portions of the virtual address space are stored on disk. By performing "page swapping", the storage facilities of the disk drive can be used to provide a very large memory space for the processing unit at a cost that is significantly less than if the same size memory was implemented entirely with DRAM devices.
Computers today most often have an architecture based on the Von Neumann model of computation, characterized by the storing of instruction words and data within a single, common memory space. In such "single store" computers, therefore, the execution of one machine-level instruction may involve several accesses to main memory. A single ADD instruction, for example, might require one memory access to obtain the ADD opcode, one or more memory accesses to obtain each of the two operands to be added, and one memory access to store the result. Clearly, the execution of an entire program can involve a great many memory accesses.
Since only a portion of the entire virtual memory space can be stored in main memory at one time, some memory accesses will be requested for which the desired location must first be read from the disk drive and stored in a main memory, location, replacing data previously stored there. Typically, a computer's operating system (and perhaps hardware associated with the microprocessor) performs the function of coordinating the efficient swapping of virtual memory pages between main memory and disk storage.
Typically, desktop or portable computers with disk drive units are provided with means such as an L.E.D. (light emitting diode) for indicating when the disk drive is "active", i.e., currently engaged in storing or retrieving data. Since most operations executed by the computer require access to some portion of memory, a disk drive activity indicator can give a computer user a relative measure of the efficiency of the computer's virtual memory management and a general idea of the amount of computing activity currently taking place in the computer. In extreme cases, a disk drive activity indicator could alert a user to potential problems with a computer or computer program, such as when indicating a complete lack of activity, or when indicating an overloading of the system. Some users rely upon the LED indicator light as a rough check on the proper operation of the computer or indication of the progress of the applications program being executed. For example, if the user executes a "save file" operation, and the LED does not light up to show that the file has been saved to disk, then the user is alerted to look for the reason.
Disk drive units can be located external to a desktop computer, connected by a cable, or inside the computer's housing, connected directly to a the mother board by ribbon cable. Since "floppy disk" drives and the like must be readily accessible to the user for the insertion of disks, computers are usually designed with a front-facing panel arrangement for the internal mounting of these disk drives.
Hard disk drives, on the other hand, need not be readily accessible during normal operation of the computer, since they usually do not have removable storage media. Nonetheless, hard disk drives are also commonly found mounted near the front of a computer, perhaps near or taking the place of a floppy disk drive. When mounted in such a location, a disk drive activity indicator, such as a light-emitting diode (LED) or the like, can be an integral part of the disk drive itself and still be readily visible to the user. The activity indicator may be attached to one of various points within the circuitry of the disk drive assembly so that it is automatically activated in response to any drive activity.
If a hard disk drive were installed on the side or rear of a computer's housing, however, an activity indicator light mounted directly on the disk drive would not be visible to the user, and therefore would be of little or no use. Accordingly, a drive not mounted in a user-visible location must be provided with a remotely-located activity indicator on or near the front of the computer housing.
In response to the increasing and widespread popularity of desktop size computers, computer manufacturers have made significant advances in the design and manufacturing techniques for their products, enabling them to maximize productivity while minimizing cost of production. Surface-mount technology (SMT) devices and flow-soldering techniques have led to partially or fully automated computer assembly lines. Such advances have resulted in smaller, more reliable and less expensive computers. For this reason, it is particularly undesirable to include in a computer a disk drive activity indicator on the front panel that requires a wire to connect it to a rear-mounted disk drive. Such a design would have the effect of slowing the assembly process for the computer and increasing both the parts cost and the assembly cost.
As an alternative to having a wire that directly connects an indicator LED to a rear-mounted disk drive, the LED could instead be connected to some other system component that is closer to the desired location of the LED, provided that the LED was still triggered in response to drive activity. For example, the indicator could be attached directly to the motherboard of the computer, near the front of the computer and visible to the user through an appropriately positioned aperture in the computer's front panel. In one prior method, such an LED is coupled to a bit position in a dedicated register on the motherboard; the operating system disk driver routines set this bit just before every disk drive access, and reset the bit upon completion of the access. In this way, the indicator LED is mounted, without additional wire, directly to the motherboard, and can accurately reflect disk drive activity.
A disadvantage to the external indicator light implementation just described, however, is that the triggering of the LED is dependent upon an explicit single-purpose action that does not by necessity occur with each disk access. That is, it is possible for disk driving software to initiate a disk access without setting the bit in the dedicated register, whereas with a drive having an internally connected indicator LED, access to the drive is typically not possible without activating the indicator LED.
It is accordingly a feature of the present invention to provide a drive activity indicator located in a position remote from the drive unit itself; another feature is that this indicator is triggered, without explicit action being taken by the CPU, in response to any drive activity. It is a further feature of the present invention that installation of the activity indicator does not require a dedicated, direct connection between the indicator and the drive. An additional feature is the provision of a remote indicator light, useful for rear-mounted hard disk drives or the like, which does not increase the parts cost or assembly cost by any significant amount.